The main radiological finding of a unicompartment osteoarthritis of the knee is the loss or decrease in the articular cartilage space. The secondary findings are spur formation and/or synovitis of the knee. The articular cartilage that is lost in the knee generally occurs in either one of two ways; first in the medial joint and then extending to the patellofemoral joint and eventually to the lateral joint. When this situation occurs the patient has a varus deformity of the knee. The other situation that occurs is a loss of the lateral joint articular cartilage initially, then loss of the patellofemoral cartilage space, and eventually, loss of the medial joint compartment space. In this situation one has a valgus deformity of the knee. Present also in a primary osteoarthritis or unicompartment arthritis of the knee is loss of the meniscal space due to an extrusion of the meniscus and/or tears of the meniscus. In other words, generally there is a primary loss of the articular cartilage followed by secondary degenerative changes of the menisci.
The other situations that can occur are a primary tear of the lateral meniscus which can lead to lateral joint arthritis, or tear of the medial meniscus leading to secondary osteoarthritis of the medial joint. The latter situation often occurs in traumatic injuries in young people who later on develop osteoarthritis of the knee. In both situations, the end result is that there is a loss or decrease in either the medial or lateral joint space with associated tearing or extrusion of the medial meniscus or lateral meniscus.
There are ways to prevent or treat the collapse of the medial and lateral joint. The present techniques include a unispacer, a unicompartment knee replacement, a meniscal transplant or allograft, a high tibial osteotomy, and/or an unloading external brace. All of these techniques seek to prevent further collapse of the medial and lateral joints, i.e., they provide for decompression of the medial and lateral joints. All of these methods except for bracing have limitations in that they do not encourage replenishment or regeneration of the articular cartilage but rather replace the surface of the articular cartilage.
An object of the invention is to provide an internal brace for the medial and/or lateral joint of the knee which will prevent this process from progressing.
Another object is to provide an internal knee brace which will provide for decompression of the medial and/or lateral joints without removing or replacing articular cartilage.
A still further object of the invention is to provide an internal brace for a knee joint in which the adjacent joint surfaces are forced apart in order to give the cartilage between the surfaces a chance to regenerate.